1. Field of the Invention
This invention relates to a transmitter, a receiver, a transmitting method and a receiving method, and more particularly, is suitably applied to, for instance, the terminal units of a video conference system.
2. Description of the Related Art
In a video conference system, a plurality of terminal units is provided at a number of spots and connected together through public network. Moving image data and audio data are transmitted and received among those terminal units so that a conference can be carried out by employing moving images on the basis of the moving image data and sound on the basis of the audio data.
In practice, in a video conference system, the moving image data and the audio data to be transmitted in each terminal unit are subjected to coding processing in accordance with applied prescribed coding modes. The obtained coded moving image data and the coded audio data are transmitted to other terminal units through public network. The terminal unit which receives these coded moving image data and coded audio data performs decoding processing on them in accordance with proper decoding modes, so that original moving image data and audio data can be obtained.
In this case, for some of such video conference systems, coding and decoding modes of the moving image data standardized on the basis of an advice called xe2x80x9cH. 261xe2x80x9d by the international telecommunication union-telecommunication standardization sector (ITU-T) are applied to each terminal unit.
The video conference system with the above-described configuration is so defined as to code the moving image data in a first image format called a common intermediate format (CIF) of 352 pixels in the horizontal direction and 288 lines in the vertical direction on the basis of the xe2x80x9cH. 261.xe2x80x9d
Therefore, in the video conference system with the abovedescribed configuration, even in the case that each terminal unit is installed in a country where a television system such as the national television system committee (NTSC) system (720 pixels in the horizontal direction and 240 lines in the vertical direction) and the phase alternation by line (PAL) system (720 pixels in the horizontal direction and 288 lines in the vertical direction)to which a different image format is applied is adopted, the image format of moving image data formed in accordance with this television system is converted into the first image format, then, the moving image data with its converted image format is subjected to coding processing and the obtained coded moving image data is transmitted to other terminal units through public network.
Further, in the video conference system, the above coded moving image data is subjected to decoding processing in the terminal unit which receives the coded moving image data, then, the first image format thereof is converted into the image format of a relevant television system. In this way, the moving image data can be transmitted and received irrespective of the television system.
In the video conference system with such a configuration, however, since the image format of the moving image data having relatively high resolution which is formed on the basis of a prescribed television system is converted into the first image format upon transmission of data, the resolution for this moving image data lowers. As a consequence, even if it is desired to transmit and receive the moving image data corresponding to the moving image with high resolution, it is impossible to meet this demand.
As a kind of these video conference systems known in the art, coding and decoding modes standardized in accordance with an advice called xe2x80x9cH. 261 Annex Dxe2x80x9d on the basis of the xe2x80x9cH. 261xe2x80x9d by the ITU-T are applied to each terminal unit.
The video conference system with the above-mentioned configuration is so defined as to transmit and receive still image data corresponding to the still image in an image format (referred to as a second image format, hereinafter) four times (704 pixels in the horizontal direction and 576 lines in the vertical direction) as high as the first image format as well as to transmit and receive the moving image data in the first image format.
Actually, in the video conference system with the above configuration, each terminal unit is designed to divide, upon transmission of the still image data, the still image data into four pieces of first to fourth still image data having an image size which corresponds to that in the first image format (referred to as first to fourth split still image data, hereinafter), then sequentially apply coding processing thereto, and transmit the obtained first to fourth coded split still image data, and to apply, upon receiving the still image data, decoding processing to the first to fourth received split still image data and reproduce original still image data on the basis of the obtained first to fourth split still image data.
Therefore, while it has recently been considered in the video conference system with the above configuration that the moving image data in the second image format corresponding to moving images having higher resolution is transmitted and received under the transmitting and receiving processing of the still image data, it is difficult to transmit and receive the moving image data in the second image format, because the xe2x80x9cH. 261 Annex Dxe2x80x9d specifies that the still image data (composed of one frame) must not be transmitted successively for two frames or more.
In view of the foregoing, an object of the present invention is to provide a transmitter, a receiver, a transmitting method and a receiving method which are capable of transmitting and receiving moving image data with higher resolution than that of moving image data which is specified by prescribed coding and decoding modes.
The foregoing object and other objects of the invention have been achieved by the provision of a transmitter for coding the first moving image data in a prescribed first image format with a prescribed coding mode and transmitting the coded moving image data, dividing the still image data of a second image format having a larger image size than that in the first image format into a plurality of split still image data with an image size corresponding to that in the first image format, and then, subjecting the split still image data to the coding processing and transmitting the coded split still image data. The transmitter comprises:
moving image data dividing means for sequentially dividing the second moving image data in the second image format into a plurality of split moving image data with an image size corresponding to that in the first. image format on the basis of unit of frame, and sequentially and alternately outputting the split moving image data for one frame out of the second moving image data and the dummy moving image data for at least one frame with an image size corresponding to that in the first image format; and
coding means for coding the split moving image data and the dummy moving image data outputted from the moving image data dividing unit.
As a result, the second moving image data can be transmitted with ease in accordance with the prescribed coding mode without converting the second image format of the second moving image data into the first image format.
Further, according to the present invention, there is provided a receiver for receiving and decoding with a relevant decoding mode first moving image data and each split still image data coded by and transmitted from the transmitter which codes and transmits the first moving image in a prescribed first image format with a prescribed coding mode, divides still image data in a second image format having a larger image size than that in the first image format into a plurality of split still image data with an image size corresponding to that in the first image format, subjects split still image data to coding processing and transmits coded split still image data. The receiver comprises: receiving means for receiving split moving image data and dummy moving image data, which are obtained after second moving image data in the second image format is sequentially divided on the basis of unit of frame into a plurality of split moving image data with an image size corresponding to that in the first image format, and the split moving image data for one frame out of the second moving image data for at least one frame with an image size corresponding to that in the first image format are sequentially and alternately coded by and transmitted from the transmitter; decoding means for decoding each coded split moving image data and the dummy moving image data which are coded and received by the receiving unit and alternately outputting in sequence each split moving image data and the dummy moving image data which are thus obtained; moving image data integrating means for selectively using and integrating the split moving image data of the split moving image data and the dummy moving image data which are outputted from the decoding unit to reproduce the second moving image data.
As a consequence, the second moving image data transmitted from the transmitter in accordance with the prescribed coding mode without converting the second image format into the first image format can be received and processed with ease.
Further, according to the present invention, there is provided a transmitting method for coding the first moving image data in a prescribed first image format with a prescribed coding mode and transmitting the coded moving image data, dividing the still image data in a second image format having a larger image size than that in the first image format into a plurality of split still image data with an image size corresponding to that in the first image format, and then, subjecting the split still image data to the coding processing and transmitting the coded split still image data. The transmitting method comprises: a first step of sequentially dividing the second moving image data in the second image format into a plurality of split moving image data with an image size corresponding to that in the first image format on the basis of unit of frame, and alternately outputting in sequence each split moving image data for one frame out of the second moving image data and the dummy moving image data for at least one frame with an image size corresponding to that in the first image format; and a second step of coding each split moving image data and the dummy moving image data outputted in the first step.
Consequently, the second moving image data can easily be transmitted in accordance with the prescribed coding mode without converting the second image format of the second moving image data into the first image format.
Further, according to the present invention, there is provided a receiving method for receiving and decoding with a relevant decoding mode first moving image data and each split still image data coded by and transmitted from the transmitter which codes and transmits the first moving image in a prescribed first image format with a prescribed coding mode, divides still image data in a second image format having a larger image size than that in the first image format into a plurality of split still image data with an image size corresponding to that in the first image format, subjects split still image data to coding processing and transmits coded split still image data. This receiving method comprises: a first step of receiving split moving image data and dummy moving image data, which are obtained after second moving image data in the second image format is sequentially divided on the basis of unit of frame into a plurality of split moving image data with an image size corresponding to that in the first image format, and the split moving image data for one frame out of the second moving image data for at least one frame with an image size corresponding to that in the first image format are sequentially and alternately coded by and transmitted from the transmitter; a second step of applying the decoding processing to each coded split moving image data and the coded dummy moving image data that are received in the first step and alternately outputting in sequence each split moving image data and the dummy moving image data which are thus obtained; and a third step of selectively using and integrating the split moving image data from the split moving image data and the dummy moving image data which are outputted in the second step so as to reproduce the second moving image data.
As a result, the second moving image data transmitted from the transmitter in accordance with the prescribed coding mode without converting the second image format into the first image format can be received and processed with ease.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.